The present invention relates generally to an extended bandwidth semiconductor optical amplifier.
In optical communication systems, optical amplifiers play an important role in compensating for losses in multiplexing, splitting, switching, or wavelength converting. Semiconductor optical amplifiers (SOA""s) are used widely to meet these needs. The use of SOA""s is advantageous because they are less expensive and smaller than fiber amplifiers. One problem associated with conventional SOA""s, however, is that their gain spectrum is narrow, typically around thirty to forty nanometers wide. Because of their narrow gain spectrum, the usefulness of conventional SOA""s is somewhat limited in WDM (Wavelength Divisional Multiplexing) applications.
Accordingly, there exists a need for an optical amplifier whose gain spectrum is wider so as to cover as much of the useful fiber-optic communications spectrum as possible.
The present invention provides a semiconductor optical amplifier (SOA) with a wide gain spectrum. In one embodiment, the SOA has Multiple Quantum Well (MQW) stacks whose thickness varies along the length of the device. The gain spectrum of this embodiment is flatter and broader than conventional SOA""s that are constructed using MQW stacks of uniform thickness.
Many semiconductor fabrication techniques can be used to fabricate the extended bandwidth SOA. Selective area growth is a technique that allows the growth rate to be varied as a function of position due to the proximity of a mask. When the gap between the masked areas is small the growth rate is highest. This results in thicker MQW stacks that have a gain peak at shorter wavelengths. In some embodiments where the MQW stacks are thicker at one end than at another, the cross-sectional area of the MQW stacks perpendicular to the propagation direction of optical signals remains largely constant.